The present disclosure relates to a display unit and an electronic apparatus that include a thin film transistor (TFT) using an oxide semiconductor as a channel.
Recently, organic electroluminescence (EL) display units using an organic EL device have been attracting attention as alternative display units to liquid crystal display units. The organic EL display units are self-luminous type display units, and have a characteristic of low power consumption. Moreover, the organic EL display units have advantages of a wide viewing angle, excellent contrast, and fast response speed; therefore, the organic EL display units have been attracting attention as next-generation flat display units. In particular, development of active matrix (AM) organic EL display units in which a TFT is provided to each pixel to control light emission and a light emission level has been advanced.
Most of TFTs used in the above-described display units often use amorphous silicon, polycrystalline silicon, and the like as a channel (a semiconductor layer); however, recently, a technique to apply a TFT using an oxide semiconductor to an electronic device or an optical device has been attracting attention. For example, in a semiconductor unit in Japanese Unexamined Patent Application Publication No. 2007-123861, a TFT using an oxide semiconductor such as zinc oxide or an In—Ga—Zn—O-based oxide as a switching device of each pixel is disclosed.
The TFT including a semiconductor layer formed of the oxide semiconductor is susceptible to hydrogen. More specifically, a threshold voltage is shifted toward a negative direction to cause deterioration in characteristics of the TFT, because hydrogen serves as a donor to release electrons as carriers, thereby forming a channel in the semiconductor layer without applying a voltage to a gate electrode. For example, Japanese Unexamined Patent Application Publication No. 2008-141119 indicates that, when hydrogen is added to an oxide semiconductor film, electrical conductivity is increased by about 4 to 5 digits. Moreover, it is described that hydrogen is diffused into the oxide semiconductor film from an insulating film in contact with the oxide semiconductor film. Thus, the oxide semiconductor is extremely sensitive to hydrogen, and even a small amount of hydrogen included in the TFT may affect the characteristics of the TFT.
On the other hand, for example, in semiconductor units in Japanese Unexamined Patent Application Publication Nos. 2012-216792, 2012-216793, 2012-216794, and 2012-216795, a laminate film formed by laminating a hydrogen permeable film and a hydrogen capture film in order from an oxide semiconductor film is formed as a gate insulating film below the oxide semiconductor film. In the semiconductor units, hydrogen released from the oxide semiconductor film during heat treatment is captured by the hydrogen capture film, and a concentration of hydrogen in proximity to an interface of the oxide semiconductor film is reduced to secure the characteristics of the TFT.